In the present situation, the implementation of Smart Grids is one of the pressing challenges in the energy field, both for the improvement in efficiency it implies, as for its positive effects on the environment, since they facilitate the massive incorporation of renewable energy into the system. One problem that arises in the management of these networks is to simulate in realtime their associated load-flow problems, which allow the knowledge of the grid status and to respond in real time to manage power demands. This thesis examines how losses are evaluated in a network, that is, the difference between the generated and consumed power, when a photovoltaic generator is incorporated in one of its nodes. The needed calculations are explained, as well as the nonlinear system to solve, taking as test system a grid consisting of a three-phase generator, a transformer, and 100 equidistant nodes.